Joseph Emilio "Jun" Aguinaldo Abaya is a Filipino politician, lawyer, and military officer. He was the Secretary of the Department of Transportation and Communications (DOTC) of the Philippines under the administration of President Benigno Aquino III. A member of the Liberal Party, he has been elected to three terms as a member of the Philippine House of Representatives, representing the 1st District of Cavite. He first won election to the House in 2004, and was re-elected in 2007. He and other Aquino administration officials have been charged over the alleged anomalous contracts for the MRT Line 3 during their tenure.

The Metro Rail Transit Line 3, also known as the MRT Line 3, MRT-3 or Metrostar Express, is a light rapid transit system line of Metro Manila, the Philippines.